The goal of this study was to determine whether use of postmenopausal estrogen (Premarin®, Wyeth-Ayerst, Philadelphia, PA) in women with autosomal dominant polycystic kidney disease (ADPKD) increases liver, hepatic cyst, or kidney volume. We also determined whether clinical symptoms correlated with the volume of either the liver or kidneys. Eight women off estrogen (control, C) and 11 others on estrogen (Premarin®, E) were studied basally and after 1 year. The two groups were similar in age, weight, age at menarche, and gravida. Volumes of total liver, hepatic cysts, hepatic parenchyma, and total kidney were measured by a validated computed tomography (CT) technique. Estrogen treatment was associated with a selective increase in total liver volume (E vs. C: Δ = 7% ± 12% vs. -2% ± 8%, P < .03) and no change in kidney volume (E vs. C: Δ = 0% ± 6% vs. -2% ± 6%, P = NS). Symptoms were common, regardless of estrogen treatment (abdominal pain 60%, shortness of breath 40%, or both 35%). Patients with symptoms of abdominal pain and shortness of breath had significantly increased hepatic volumes (P < .03) but similar kidney volume compared with patients without symptoms. We conclude that estrogen treatment of postmenopausal ADPKD women is associated with selective liver enlargement and that abdominal symptoms in ADPKD patients may be because of extensive hepatic cystic disease.